import java.io.*;
import java.util.*;

class qiuC {
	public int getC(int n,int m) {
		if(n<0 || m<0) {
			return 0;
		}
		if(n<m||m==0) {
			return 0;
		}
		if(n == m) {
			return 1;
		}
		if(m == 1) {
			return n;
		}
		else {
			return getC(n-1,m-1)+getC(n-1,m);
		}
	}
}

public class C {
	public static void main (String args[]) {
		Scanner sc = new Scanner(System.in);
		int [] n=new int [args.length];
		int i;
		for (i=0; i<args.length; i++){
			n[i] = Integer.parseInt(args[i]);
		}
		qiuC qiu = new qiuC();
		int fin = qiu.getC(n[0],n[1]);
		System.out.printf("%d\n",fin);
	}
}

